First Results of the QUENCH-ALISA Bundle Test

The bundle experiment QUENCH-18 on air ingress and aerosol release was successfully conducted at KIT in the frame of the EC supported ALISA program. The primary aims were to examine the oxidation of M5® claddings in air/steam mixture following a limited pre-oxidation in steam, and to achieve a long period of oxygen and steam starvations to promote interaction with the nitrogen. Additionally, the QUENCH-18 experiment investigated the effects of the presence of two Ag-In-Cd control rods, and two pressured unheated rod simulators (60 bar, He). The low-pressurized heater rods (2.3 bar, similar to the system pressure) were Kr-filled. In a first transient, the bundle was heated in an atmosphere of flowing argon and superheated steam by electrical power increase to the peak cladding temperature of 1400 K. During this heat-up, claddings of the two pressurized rods were burst at temperature of 1045 K. The attainment of 1400 K marked the start of the pre-oxidation phase to achieve a maximum cladding oxide layer thickness of about 100 µm. In the air ingress phase, the steam and argon flows were reduced, and air was injected. The first Ag-In-Cd... mehr aerosol release was registered at 1350 K and was dominated by Cd bearing aerosols. Later in the transient, a significant release of Ag was observed. A strong temperature escalation started in the middle of the air ingress phase. Later a period of oxygen starvation occurred and was followed by almost complete steam consumption and partial consumption of the nitrogen. Following this, the temperatures continued to increase and stabilized at melting temperature of Zr bearing materials until water injection. Almost immediately after the start of reflood there was a temperature excursion, leading to maximum measured temperatures of about 2450 K. Final quench was achieved after about 800 s. A significant quantity of hydrogen was generated during the reflood (238 g). Nitrogen release (>54 g) due to re-oxidation of nitrides was also registered.